To find the radius of the original circle before applying the scale factor of 1/5, you can set up the equation:
\[ \text{New radius} = \text{Original radius} \times \text{Scale factor} \]
In this case, the new radius is 18 cm and the scale factor is 1/5. Let \( r \) be the original radius:
\[ 18 \text{ cm} = r \times \frac{1}{5} \]
To solve for \( r \), multiply both sides by 5:
\[ r = 18 \text{ cm} \times 5 = 90 \text{ cm} \]
So, the radius of the original circle is 90 cm.
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